The present invention relates to an optoelectronic microelectronic system.
In microelectronics, alongside purely electronic systems such as integrated semiconductor circuits in which electronic functional units, such as transistors, diodes, capacitors, etc., are integrated in a semiconductor substrate, it has become standard to combine optical elements as well with the electronic functional units. Here, modern semiconductor technology makes it possible to monolithically integrate photosensors, in the form of photodiodes and light waveguides, with electronic systems, such as for example amplifiers. This can for example take place in MOS technology, whereby the process of manufacture of photosensors in the form of photodiodes and light waveguides is compatible with the process of manufacture of the electronic amplifier functional units.
An optoelectronic microelectronic system of the type cited above is known in principle from the reference titled xe2x80x9cMicroelectronic Engineeringxe2x80x9d 15 (1991), pp. 289-292. On the basis of an integrated structure in CMOS technology, having an NMOS transistor and a PMOS transistor as well as a photodiode, this reference explains the technology for a monolithic integration.
A known photodiode is formed in a silicon substrate of one conductivity type, having weak doping, e.g. of the p-conductivity type. Trench insulators are provided for insulation against electronic functional units, such as the above-mentioned MOS transistors. The insulators can be what are known as shallow trench isolation (STI) regions with silicon dioxide. In a region between the trench insulators, a first zone having one conductivity type, i.e. for example the p-conductivity type, is provided, as well as a second zone of the opposite conductivity type, i.e. for example the n-conductivity type, the zones having a high doping concentration in comparison with the doping concentration of substrate. The expression xe2x80x9cweak dopingxe2x80x9d used above for the substrate doping thus denotes a low doping concentration in comparison with the doping concentration of zones. A weakly doped zone, which in practice can also be designated an intrinsic zone, is thus located between the first and second zones. If, as is standard, a low doping concentration is designated by a minus sign, and a high doping concentration is designated by a plus sign, then for the above conductivity types, given as examples, for the substrate as well as the zones an optoelectronically active diode part results having the zone sequence: p+-first zone, pxe2x88x92-intrinsic zone, and n+second zone.
On the substrate having the trench insulators and the zones, a light waveguide is provided that can be made for example of silicon oxide nitride/silicon dioxide. From a light wave running in the light waveguide, light is coupled into the W optoelectronically active diode part through a leaky wave coupling. Of course, light is also coupled in via the regions of the first and second zones. The coupled-in light generates charge bearers in the intrinsic zone, which in turn generate the diode photocurrent.
A photodiode of the type explained above represents a lateral, or planar, diode. In order to enable realization of a good luminous efficacy, and thus a larger photocurrent, the surface of the optoelectronically active diode part must be as large as possible, as seen in the lateral direction. However, this results in that such planar photodiodes in an integrated system require a comparably large chip surface, which has an adverse effect on the integration density. For large-scale-integrated systems, the tendency is towards ever-smaller structures, for example MOS transistors having ever-smaller channel lengths. The chip surface obtained in this way is then at least partially again destroyed through planar photodiodes. This is in particular also an economic disadvantage, because chip surface area is an essential cost factor.
In Published, Non-Prosecuted German Patent Application DE 26 24 436 A1, a photodiode structure is shown in which, in order to improve the light coupling, a structure in the shape of a mesa is fashioned that stands out from a substrate. The light couples into the mesa with its vertical component, so that the degree of coupling is increased. The mesa is formed in an epitaxial layer. A comparable photodiode structure is taught in German Patent DE 39 20 219 C2.
It is accordingly an object of the invention to provide an optoelectronic microelectronic system which overcomes the above-mentioned disadvantages of the prior art devices of this general type, that saves chip surface area in relation to a predetermined luminous efficacy, and which in addition is compatible with MOS technologies for transistor structures, in particular smaller channel lengths.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optoelectronic microelectronic system. The system contains a semiconductor substrate having a surface, a doped well formed in the semiconductor substrate and has a given conductivity type, and a mesa having a side wall and extends out vertically from the semiconductor substrate. The mesa has a part with the given conductivity type and an equivalent doping concentration as the doped well. An integrated photodiode having an optoelectronically active part is formed by doping regions that form depletion layers, and are disposed partly in the mesa and partly in the doped well. An integrated light waveguide is disposed on the doped well and surrounds the mesa so that light is coupled into the optoelectronically active part both through the side wall of the mesa and also through the surface of the doped well.
In accordance with an added feature of the invention, the optoelectronically active part includes a first zone that is disposed at an end of the mesa facing away from the semiconductor substrate. The first zone has a doping of another conductivity type being opposite to the given conductivity type. The optoelectronically active part includes a second zone disposed in the doped well at the surface of the semiconductor substrate. The second zone has the given conductivity type and a doping in a higher concentration than the doped well. The optoelectronically active part also includes the part of the mesa.
In accordance with an additional feature of the invention, the first zone is made of a silicide.
In accordance with another feature of the invention, the first zone has a higher doping concentration in comparison with the doped well.
In accordance with a further feature of the invention, the optoelectronically active part includes a first zone having a doping that produces the given conductivity type, and a doping concentration that is higher in comparison to the doped well. A second zone having a doping producing another conductivity type that is opposite to the given conductivity, and a doping concentration that is higher in comparison to the doped well. The optoelectronically active part further contains the part of the mesa. The first zone and the second zone respectively are disposed on the side wall of the mesa as well as on the surface of the doped well.
In accordance with another added feature of the invention, the integrated light waveguide surrounds the mesa in an annular fashion.
In accordance with a concomitant feature of the invention, a vertical MOS field-effect transistor is provided. The transistor contains a further well having a first conductivity type and formed in the semiconductor substrate, and a further mesa extending out from the semiconductor substrate in a region of the further well. The further mesa has a further part with the first conductivity type. The transistor has a first doping region with a second conductivity type opposite to the first conductivity type and is disposed on the surface of the further well. The transistor has a second doping region with the second conductivity type and is disposed on an end of the further mesa facing away from the semiconductor substrate. A spacer formed of silicon is disposed on a side wall of the further mesa and is insulated against the further part of the further mesa.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an optoelectronic microelectronic system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.